This 405 MW dam is the first run of the river project to come up in the state. Here is how it works. The dam wall stops the river from flowing as before. To generate power, the river water is instead channeled into a tunnel that drops 600 metres over its 10 km length eventually hitting the turbines waiting to be spun by the momentum of the water.

There are two things to be kept in mind here. One. The capacity of the tunnel is 160 cumecs. If the amount of water entering the reservoir is less than 160 cumecs, as in the winter months, no water is released into the Ranganadi at all. On the other hand, if the river flow is greater than that, the surplus water is released into the river.

Two. Ranganadi is a transfer basin project. The tunnel opens out -- not further downstream along the Ranganadi -- but into an adjoining river called the Dikrong. To generate power, dams tend to drop water from a height to increase the speed with which they strike the turbines. In this case, the Ranganadi is too flat a river and so, the tunnel was linked to the neighbouring Dikrong to create a drop of 600 metres. In contrast, almost all the dams coming up in Arunachal are single basin projects. They will impound water. And release it only when they want to generate peaking power.

All this has meant that the dam can generate 405mw electricity. At full capacity, 160 cumecs is what the three turbines at the end of this tunnel can handle. This means that the reservoir will hold enough water to direct 160 cumecs of river flow into the tunnel. This also means no water is released into the Ranganadi at all unless more water than what the reservoir can hold is coming in. The small amount of water flowing out of the dam into the river, I am told, is leakage. The river is expected to fill up as it flows further downstream due to tributaries. Unless, of course, there is more water than needed in the reservoir. In which case it is released.

The outcome, says Tara Rimpum, the headman of Lichi village about 20 km downstream of the NEEPCO dam, is an unpredictable river. "We have had four people and 50-60 mithuns drown when the dam suddenly released water." It is an expensive loss. Each Mithun costs anywhere between Rs 50,000-70000.

When I ask the head of the dam, Saamarjit Chakrabarty, about such complaints. he says, "We have a siren system. We play that 30 minutes before releasing water."

The villagers challenge that. "The siren is only at the dam site. How do we get to hear it?"

There are other changes. There are no more fish in the river. The Gangetic dolphin, for instance, has vanished from this river. "we now have to buy fish and eat." The river is said to be pushing boulders downstream. and so, the river bed is rising as well.